The present invention relates to methods of producing amino acid metal chelates.
Divalent cation metals are known to form chelate complexes with alpha amino acids. These complexes may be obtained by reacting the cation metals with pure amino acids (e.g., single and specific amino acids, such as methionine) as ligands. Alternatively, these complexes may be obtained by reacting the cation metals with a hydrolysate of a particular protein source.
U.S. Pat. No. 5,698,724 describes a method of preparing metal amino acid complexes in which amino acids are obtained by hydrolyzing protein of vegetable or animal origin. The protein is hydrolyzed with an acid, such as hydrochloric acid, and the resulting hydrolysate is reacted with a metal species, such as zinc oxide, to obtain the amino acid complexes.
U.S. Pat. No. 6,541,051 describes a method of preparing metal amino acid complexes in which amino acids are obtained by hydrolyzing soy protein. The protein is hydrolyzed with an acid, such as hydrochloric acid, and the resulting hydrolysate is reacted with a metal species, such as zinc oxide, to obtain the amino acid complexes.
Performing acid hydrolysis of feed proteins to obtain amino acid ligands is asserted to provide an economic advantage over using pure amino acids as ligands. However, performing acid hydrolysis can be disadvantageous because the use of strong mineral acids requires special equipment and safety precautions. In addition, the dissociated anion from the strong mineral acid (e.g., sulfate or chloride) is likely to remain in the hydrolysate and dilute the amino acid metal chelate that is sought to be obtained. Efforts to remove such anions from the hydrolysate are likely to increase costs, and the by-product salt containing the anion must be disposed of in some manner. Moreover, to obtain complete hydrolysis by acid hydrolysis requires expensive high pressure tanks as well as a high input of energy as heat and pressure.
U.S. Pat. No. 6,323,354 describes a method of preparing amino acid transition metal chelates from lipoproteins and transition metal salts. Amino acids are obtained by hydrolyzing lipoproteins obtained from, e.g., fractured cell walls from microbes generated in the biological synthesis of amino acids. The lipoproteins are hydrolyzed with a strong base, such as sodium hydroxide, and the resulting hydrolysate is reacted with a metal species, such as zinc sulfate, to obtain the amino acid transition metal chelates.
Employing base hydrolysis to obtain amino acid metal chelates poses similar problems to those described above with respect to acid hydrolysis. In addition, base hydrolysis may convert amino acids from L-isomers to D-isomers, making them nutritionally unavailable for protein production.
It is known to employ enzyme hydrolysis in various particular contexts. For example, it is known to hydrolyze starch using amylitic enzymes, to hydrolyze cellulose using cellulase and to hydrolyze proteins using proteinases. As evidenced by the absence of a commercially-used process employing such means, enzyme hydrolysis is not known to be particularly effective in preparing amino acid or short peptide ligands for use in producing amino acid metal chelates.
U.S. Pat. No. 3,969,540 describes a method of preparing metal proteinates from protein hydrolysates and metal salts. Protein hydrolysates are obtained by enzymatically hydrolyzing sources of protein such as yeast. The sources of protein are hydrolyzed using proteases. Yeast is believed to be an unacceptable source of protein for use in enzymatic hydrolysis to form amino acid ligands for chelating with metals (e.g., for use in feedstuffs) because yeast has a relatively low protein content and high purine content.